Prior art burglar alarm systems in elemental forms involving glass panels have the disadvantage that sensing elements on or embedded in the glass are visible, which defeats the purpose of glass. For example, thin, electrically conductive tapes or strips have been applied to the glass periphery in a substantially complete loop. When the glass is broken, the tape is severed and an electrical circuit is broken. This initiates a chain of electrical events resulting in the production of a signal indicating that the glass has been broken. However, such tapes are usually visible. Therefore, they are positioned only around the periphery of the glass area so as not to obstruct the view. Large areas of glass are unprotected and a skilled burglar intent on entry may cut the glass while avoiding the electrically conductive tape. Alternatively, a small hole may be cut through the glass in an area where the tape is absent, through which the burglar reaches in and short circuits the tape between its entry and exit points on the glass panel. As a result, no alarm is ever produced when the glass is broken, even though portions of the tape may be severed. The metallic tape may also be unattractive, as well as obstructive, in the environment of the glass panel.
Recently, systems have been devised which respond to sounds or other vibrations produced by intruders. Unfortunately, normal ambient sounds and vibrations may be at a higher level than those caused by a burglar breaking a glass panel. Thus, many false alarms may result in such systems.
What is needed is a security window which provides protection over the entire window area and which is invisible or substantially invisible to the human eye.
Accordingly, it is an object of this invention to provide an improved security window which contains integral intruder detection sensors which are not visible.
Another object of the invention is to provide an improved security window which contains intrusion detection sensors over any desired window area without significantly affecting window transparency.
A further object of this invention is to provide an improved security window which is damage resistant and not subject to false alarms in operation.
Yet another object of this invention is to provide an improved security window which uses conventional plastic window materials and is economic to produce.